The endothermic proton transfer reaction, H2+(upsilon+)+He-->HeH+ + H(DeltaE=0.806 eV), is investigated over a broad range of reactant vibrational levels using high-resolution vacuum ultraviolet to prepare reactant ions either through excitation of autoionization resonances, or using the pulsed-field ionization-photoelectron-secondary ion coincidence (PFI-PESICO) approach. In the former case, the translational energy dependence of the integral reaction cross sections are measured for upsilon+=0-3 with high signal-to-noise using the guided-ion beam technique. PFI-PESICO cross sections are reported for upsilon+=1-15 and upsilon+=0-12 at center-of-mass collision energies of 0.6 and 3.1 eV, respectively. All ion reactant states selected by the PFI-PESICO scheme are in the N+=1 rotational level. The experimental cross sections are complemented with quasiclassical trajectory (QCT) calculations performed on the ab initio potential energy surface provided by Palmieri et al. [Mol. Phys. 98, 1839 (2000)]. The QCT cross sections are significantly lower than the experimental results near threshold, consistent with important contributions due to resonances observed in quantum scattering studies. At total energies above 2 eV, the QCT calculations are in excellent agreement with the present results. PFI-PESICO time-of-flight (TOF) measurements are also reported for upsilon+=3 and 4 at a collision energy of 0.6 eV. The velocity inverted TOF spectra are consistent with the prevalence of a spectator-stripping mechanism.

We have studied 3s(n-1 and pi-1) Rydberg states and D0(n-1) and D1(pi-1) cationic states of pyrazine [1,4-diazabenzene] by picosecond (2 + 1) resonance-enhanced multiphoton ionization (REMPI), (2 + 1) REMPI photoelectron imaging, He(I) ultraviolet photoelectron spectroscopy (UPS), and vacuum ultraviolet pulsed field ionization photoelectron spectroscopy (VUV-PFI-PE). The new He(I) photoelectron spectrum of pyrazine in a supersonic jet revealed a considerably finer vibrational structure than a previous photoelectron spectrum of pyrazine vapor. We performed Franck-Condon analysis on the observed photoelectron and REMPI spectra in combination with ab initio density functional theory and molecular orbital calculations to determine the equilibrium geometries in the D0 and 3s(n-1) states. The equilibrium geometries were found to differ slightly between the D0 and 3s states, indicating the influence of a Rydberg electron on the molecular structure. The locations of the D1-D0 and 3s(pi-1)-3s(n-1) conical intersections were estimated. From the line width in the D1 <-- S0 spectrum, we estimated the lifetime of D1 to be 12 fs for pyrazine and 15 fs for fully deuterated pyrazine. A similar lifetime was estimated for the 3s(pi-1) state of pyrazine by REMPI spectroscopy. The vibrational feature of D1 observed in the VUV-PFI-PE measurement differed dramatically from that in the UPS spectrum, which suggests that the high-n Rydberg (ZEKE) states converging to the D1 vibronic state are short-lived due to electronic autoionization to the D0 continuum.

The vacuum ultraviolet pulsed field ionization (PFI)-photoelectron (PFI-PE) spectrum of CO2 has been measured in the energy region of 19.0–20.0 eV. The PFI-PE vibrational bands resolved for CO2+(C 2Σg+) are overwhelmingly dominated by the origin band along with weak vibrational bands corresponding to excitations of the ν1+ (symmetric stretching), ν2+ (bending), and ν3+ (antisymmetric stretching) modes. The simulation of the rotational contour resolved in the origin PFI-PE band yields a value of 19.3911±0.0005 eV for the ionization energy of CO2 to form CO2+(C 2Σg+). A PFI-PE peak is found to coincide with each of the 0 K dissociation thresholds for the formation of O+(4S)+CO(X 1Σ+) and CO+(X 2Σ+)+O(3P). This observation is tentatively interpreted to result from the lifetime switching effect, arising from the prompt dissociation of excited CO2 in high-n (n⩾100) Rydberg states prior to PFI. We have also examined the decay pathways for state-selected CO2+ in the internal energy range of 5.2–6.2 eV using the PFI-PE-photoion coincidence scheme. The coincidence TOF data show unambiguously the formation of O+(4S)+CO(X 1Σ+;ν″=0,1) and CO+(X 2Σ+;ν+=0,1)+O(3P). Analysis of the kinetic energy releases of fragment ions suggests that the dissociation of excited CO2+ involved is nonstatistical and proceeds with an impulsive mechanism. Potential energy functions (PEFs) for the CO2+(C 2Σg+) state and the lowest quartet states of CO2+, together with their spin–orbit interactions, have been calculated using the complete active space self-consistent field and internal contracted multireference configuration interaction methods. Based on these PEFs, vibrational levels for CO2+(C 2Σg+) have been also calculated using a variational approach. With the aid of these theoretical calculations, vibrational bands resolved in the PFI-PE spectrum for CO2+(C 2Σg+) have been satisfactorily assigned, yielding a ν3+ value of 2997 cm−1. The theoretical calculation also provides a rationalization that the predissociation for CO2+(C 2Σg+) to form O+(4S)+CO(X 1Σ+) and CO+(X 2Σ+)+O(3P) most likely proceeds via the repulsive a 4Σg− and b 4Πu (or B14 in a bent geometry) states.

n-CdS/p-PbSe heterojunction is investigated. A thin CdS film is deposited by chemical bath deposition on top of epitaxial PbSe film by molecular beam epitaxy on Silicon. Current-voltage measurements demonstrate very good junction characteristics with rectifying ratio of $178 and ideality factor of 1.79 at 300 K. Detectors made with such structure exhibit mid-infrared spectral photoresponse at room temperature. The peak responsivity R k and specific detectivity D * are 0.055 A/W and 5.482 Â 10 8 cmÁHz 1/2 /W at k ¼ 4.7 lm under zero-bias photovoltaic mode. Temperature-dependent photoresponse measurements show abnormal intensity variation below $200 K. Possible reasons for this phenomenon are also discussed. V

Public reporting burden for this collection of inrioat ion is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, mid completing ind reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for information bimolecular ion-molecule reaction dynamics studies using pulsed field ionization (PFI) of atoms or molecules in high-n Rydberg states produced by vacuum ultraviolet (VUV) synchrotron or laser photoexcitation. Employing the pseudocontinuum high-resolution VUV synchrotron radiation at the Advanced Light Source as the photoionization source, PFI photoions (PFI-PIs) in selected rovibrational states have been generated for ion-molecule reaction studies using a fast-ion gate to pass the PFI-PIs at a fixed delay with respect to the detection of the PFI photoelectrons (PFI-PEs). The fast ion gate provided by a novel interleaved comb wire gate lens is the key for achieving the optimal signal-to-noise ratio in state-selected ion-molecule collision studies using the VUV synchrotron based PFI-PE secondary ion coincidence (PFI-PESICO) method. The most recent development of the VUV laser PFI-PT scheme for state-selected ion-molecule collision studies is also described. This paper presents the methodology to generate beams of ions in single quantum states for bimolecular ion-molecule reaction dynamics studies using pulsed field ionization (PFI) of atoms or molecules in high-n Rydberg states produced by vacuum ultraviolet (VUV) synchrotron or laser SPONSORING I MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) SPONSOR/MONITOR'S REPORT NUMBER(S)